geom怎么把Z 轴改为负数

SELECT 
  ST_AsText(ST_MakeLine(
    ST_MakePoint(ST_X(ST_PointN(geom, 1)), ST_Y(ST_PointN(geom, 1)), ST_Z(ST_PointN(geom, 1))*10),
    ST_MakePoint(ST_X(ST_PointN(geom, 2)), ST_Y(ST_PointN(geom, 2)), ST_Z(ST_PointN(geom, 2)))
  )) AS merged_line
FROM "line3d2" 
WHERE gid = 20570;

UPDATE line3d2
SET geom = ST_SetSRID(
    ST_MakeLine(
        ST_MakePoint(ST_X(ST_PointN(geom, 1)), ST_Y(ST_PointN(geom, 1)), -ST_Z(ST_PointN(geom, 1))),
        ST_MakePoint(ST_X(ST_PointN(geom, 2)), ST_Y(ST_PointN(geom, 2)), -ST_Z(ST_PointN(geom, 2)))
    ),
    ST_SRID(geom)
)
WHERE gid != 20570;